Girls who survived from what activists say is a gas attack rest inside a mosque in the Duma neighborhood of Damascus

Mohamed Abdullah / Reuters

(Mohamed Abdullah / Reuters)

The Obama administration, overcoming its sensible caution about intervening in Syria, now looks determined to take military action in response to Bashar Assad's apparent use of chemical weapons. It's obvious that whatever we do may not work. But if Obama can live with that reality, the intervention may not be too costly.

It's not clear what the point of the retaliation will be. If Obama hopes to topple Assad, he's probably going to be disappointed. If he hopes to turn the tide of the war in the rebels' favor, likewise. But maybe he just wants to show the world that no one can use chemical weapons with impunity. In that case, he can send a few cruise missiles, make his point, and be done with it.

That choice might deter Assad from repeating his war crime. But it could also backfire. Assad might decide that he'd better use all his chemical weapons right away in an effort to wipe out the opposition once and for all. If the rebels are crushed, he may figure, he'll be safe because neither the United States nor its allies will invade. That kind of victory would make him a pariah, but he's not exactly trying to win the Nobel Peace Prize.

If Obama decides to use military force, he should have in mind what he hopes to achieve and what he doesn't expect. And if it doesn't work out well, he should accept the outcome and move on.